Tests have begun on a new engine that could launch a plane into space and revolutionise the way we travel - making it possible to reach anywhere on Earth in just four hours.

The 270ft Skylon spaceplane would take off and land from a conventional runway but fly 18 miles above the ground and out of the Earth's atmosphere at five times the speed of sound.

Critical tests are now being carried out to make sure the Sabre engine - a hybrid that can operate like a normal jet engine but then switch to rocket mode - is faultless before its developers Reaction Engines Limited (REL) based in Culham, Oxfordshire, can unveil it at the Farnborough International Air Show.

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